1. Field of the Invention
The present invention relates to a player piano system provided with a performance state detecting unit capable of detecting a string-striking velocity of a hammer with accuracy.
2. Prior Art
The player piano can record and then automatically playback the performance. Recording of the performance is made by use of a sensor which detects the string-striking velocity of the hammer corresponding to the depressed key. Based on such string-striking velocity to be detected, tone color and tone volume can be determined.
FIG. 1 illustrates an example of the conventional string-striking velocity detecting unit of the player piano.
In FIG. 1, this detecting unit provides a plate-shaped hammer shutter 94 at a middle portion of a hammer shank 93 of a hammer 92 which will strike a string 91.
Each of light-transmission-type photo sensors 95A, 95B is configured by a pair of light emitting portion and light receiving portion which are respectively placed to face each other. More specifically, these portions are positioned at both sides of the plane including a rotating locus of the hammer shutter 94. In addition, the photo sensor 95A is placed in the vicinity of another photo sensor 95B. For example, these sensors 95A, 95B are fixed, along with the rotating locus of the hammer shutter, to a fixing member 96 at respective positions which are apart from each other by the predetermined distance.
Thus, in the string-striking action of the hammer 92, the hammer shutter 94 can cut off each of the light paths of the photo sensors 95A, 95B.
Therefore, accompanied with the string-striking action of the hammer 92, the revolving hammer shutter 94 will cut off each of the light paths of the photo sensors 95A, 95B in turn. Then, this unit measures the time difference between light-cut-off times of the photo sensors 95A, 95B. Based on the measured time difference, this unit computes and then records the string-striking velocity of the hammer 91.
Actually, this unit detects the rotating velocity of the hammer shank at a time in the middle of the string-striking action. However, in order to accurately detect the actual string-striking velocity of the hammer 92, the photo sensors 95A, 95B must be placed close to the string-striking position of the hammer 92 as much as possible.
In order to improve the detection accuracy, it is necessary to accurately position the light emitting portion and light receiving portion of each photo sensor; accurately set the mechanical positionings of the photo sensors 95A, 95B and hammer shutter 94; and accurately set the distance between the photo sensors 95A, 95B.
According to the convetional string-striking velocity detecting unit of the player piano, a pair of photo sensors 95A, 95B must be provided for each of eighty-eight keys. However, it is difficult to arrange these photo sensors by the predetermined constant distance for each of eighty-eight keys. Due to the deviation of the distance between them, it is impossible to compute the string-striking velocity accurately even if the foregoing time difference is measured correctly.
Further, it is necessary to correct the distance between the sensors and fixing position of the sensor which may be deviated due to the dispersion among the hammers. In this case, however, it is difficult to correctly fix the hammer shutter to the hammer shank and set the positioning of the hammer shutter with respect to the sensor. Because, in order to attach the hammer shutter to the hammer shank, it is necessary to perform the task with high accuracy. This results in an increase in the manhours required for the assembly and adjustment.
In the conventional unit, it is impossible to arrange the photo sensor close to the string-striking point, because it is impossible to provide a space for adjusting the positioning of the sensor. As a result, the conventional unit can merely detect the average rotating velocity of the hammer, thus, it is impossible to detect the actual string-striking velocity with high accuracy. In other words, the actual string-striking point of each string must be differed with respect to each string-striking mechanism, however, the conventional unit cannot adjust the fixing position of the sensor close to such string-striking point.
In short, high-accuracy positioning is required for the sensor, however, in some cases, the detected string-striking velocity is not so correct due to the dispersion among the sensors. Therefore, the conventional unit must be improved with respect to the detection accuracy.
Microscopically, when the hammer strikes the string, the hammer felt partially cuts into the string and the string is slightly deflected due to the string-striking force imparted thereto. Therefore, it is very difficult to correctly specify the string-striking point.
In order to eliminate the above-mentioned drawback, it is necessary to develop the sensor which can follow up with the rotating action of the string-striking mechanism containing the hammer, in other words, which can output a signal responsive to the variation of the distance between the sensor and its corresponding member of the string-striking mechanism. As this sensor, it is possible to adopt the so-called reflection-type photo sensor, for example.
This photo sensor is designed to output a signal of which value can be varied responsive to the variation of the distance between the sensor and member of the string-striking mechanism. This sensor provides with first and second outputs with respect to two measuring points of the member, wherein each of two measuring points has a different distance against the sensor. Based on these outputs, rotating time of the member which passes between two measuring points is measured. On the basis of the measured time and distance between two measuring points, it is possible to compute the string-striking velocity of the hammer.
However, each photo sensor may have a different output characteristic corresponding to the variation of the distance because of the different reflection rate of the light-reflecting-surface of the member and different fixing position of each photo sensor. This will cause a dispersion among the computation results of the string-striking velocity corresponding to the outputs of the sensors. For this reason, it is necessary to make a correction with respect to the dispersion among the string-striking velocities detected by respective photo sensors.